Sequence hierarchy in a Mesoproterozoic interior sag basin: from basin fill to reservoir scale,the Tombador Formation,Chapada Diamantina Basin,Brazil

The Tombador Formation exhibits depositional sequence boundaries placed at the base of extensive amalgamated fluvial sand sheets or at the base of alluvial fan conglomeratic successions that indicate basinward shifts of facies. The hierarchy system that applies to the Tombador Formation includes sequences of different orders, which are defined as follows: sequences associated with a particular tectonic setting are designated as ‘first order’ and are separated by first‐order sequence boundaries where changes in the tectonic setting are recorded; second‐order sequences represent the major subdivisions of a first‐order sequence and reflect cycles of change in stratal stacking pattern observed at 10² m scales (i.e., 200–300 m); changes in stratal stacking pattern at 10¹ m scales indicate third‐order sequences (i.e., 40–70 m); and changes in stratal stacking pattern at 10⁰ m scales are assigned to the fourth order (i.e., 8–12 m). Changes in palaeogeography due to relative sea level changes are recorded at all hierarchical levels, with a magnitude that increases with the hierarchical rank. Thus, the Tombador Formation corresponds to one‐first‐order sequence, representing a distinct intracratonic sag basin fill in the polycyclic history of the Espinhaço Supergroup in Chapada Diamantina Basin. An angular unconformity separates fluvial‐estuarine to alluvial fan deposits and marks the second‐order boundary. Below the angular unconformity the third‐order sequences record fluvial to estuarine deposition. In contrast, above the angular unconformity these sequences exhibit continental alluvial successions composed conglomerates overlain by fluvial and eolian strata. Fourth‐order sequences are recognized within third‐order transgressive systems tract, and they exhibit distinct facies associations depending on their occurrence at estuarine or fluvial domains. At the estuarine domain, they are composed of tidal channel, tidal bar and overlying shoreface heterolithic strata. At the fluvial domain the sequences are formed of fluvial deposits bounded by fine‐grained or tidal influenced intervals. Fine grained intervals are the most reliable to map in fourth‐order sequences because of their broad laterally extensive sheet‐like external geometry. Therefore, they constitute fourth‐order sequence boundaries that, at the reservoir approach, constitute the most important horizontal heterogeneity and, hence, the preferable boundaries of production zones. The criteria applied to assign sequence hierarchies in the Tombador Formation are based on rock attributes, are easy to apply, and can be used as a baseline for the study of sequence stratigraphy in Precambrian and Phanerozoic basins placed in similar tectonic settings.     

How well do integrated assessment models simulate climate change?

Integrated assessment models (IAMs) are regularly used to evaluate different policies of future emissions reductions. Since the global costs associated with these policies are immense, it is vital that the uncertainties in IAMs are quantified and understood. We first demonstrate the significant spread in the climate system and carbon cycle components of several contemporary IAMs. We then examine these components in more detail to understand the causes of differences, comparing the results with more complex climate models and earth system models (ESMs), where available. Our results show that in most cases the outcomes of IAMs are within the range of the outcomes of complex models, but differences are large enough to matter for policy advice. There are areas where IAMs would benefit from improvements (e.g. climate sensitivity, inertia in climate response, carbon cycle feedbacks). In some cases, additional climate model experiments are needed to be able to tune some of these improvements. This will require better communication between the IAM and ESM development communities.     

The Interaction Between Coronal Mass Ejections and Streamers: A Statistical View over 15 Years (1996 – 2010)

We report on the statistical analysis of the interaction between coronal mass ejections (CMEs) and streamers based on 15 years (from 1996 to 2010 inclusive) of observation of the solar corona with the LASCO-C2 coronagraph. We used synoptic maps and improved the method of analysis of past investigations by implementing an automatic detection of both CMEs and streamers. We identified five categories of interaction based on photometric and geometric variations between the pre- and post-CME streamers: “brightening”, “dimming”, “emergence”, “disappearance”, and “deviation”. A sixth category, “no change”, included all cases where none of the above variations is observed. A “global set” of 21?242 CMEs was considered as well as a subset of the 10 % brightest CMEs (denoted “top-ten”) and three typical periods of solar activity: minimum, intermediate, and maximum. We found that about half of the global population of CMEs are not associated with streamers, whereas 93 % of the 10 % brightest CMEs are associated. When there is a CME-streamer association, approximately 95 % of the streamers experience a change, either geometric or radiometric. The “no change” category therefore amounts to approximately 5 %, but this percentage varies from 1?–?2 % during minimum to 7?–?8 % during intermediate periods of activity; values of 3?–?5 % are recorded during maximum. Emergences and disappearances of streamers are not dominant processes; they constitute 16?–?17 % of the global set and 23 % (emergence) and 28 % (disappearance) of the “top-ten” set. Streamer deviations are observed for 57 % and 70 % of, respectively, the global set and “top-ten” CMEs. The cases of dimming and brightening are roughly equally present and each case constitutes approximately 30?–?35 % of either set, global or “top-ten”.     

Spatial vent opening probability map of Etna volcano (Sicily, Italy)

We produce a spatial probability map of vent opening (susceptibility map) at Etna, using a statistical analysis of structural features of flank eruptions of the last 2?ky. We exploit a detailed knowledge of the volcano structures, including the modalities of shallow magma transfer deriving from dike and dike-fed fissure eruptions analysis on historical eruptions. Assuming the location of future vents will have the same causal factors as the past eruptions, we converted the geological and structural data in distinct and weighted probability density functions, which were included in a non-homogeneous Poisson process to obtain the susceptibility map. The highest probability of new eruptive vents opening falls within a N-S aligned area passing through the Summit Craters down to about 2,000?m?a.s.l. on the southern flank. Other zones of high probability follow the North-East, East-North-East, West, and South Rifts, the latter reaching low altitudes (～400?m). Less susceptible areas are found around the faults cutting the upper portions of Etna, including the western portion of the Pernicana fault and the northern extent of the Ragalna fault. This structural-based susceptibility map is a crucial step in forecasting lava flow hazards at Etna, providing a support tool for decision makers.     

GPS network monitors the Western Alps' deformation over a five-year period: 1993–1998

  The Western Alps are among the best studied collisional belts with both detailed structural mapping and also crustal geophysical investigations such as the ECORS and EGT seismic profile. By contrast, the present-day kinematics of the belt is still largely unknown due to small relative motions and the insufficient accuracy of the triangulation data. As a consequence, several tectonic problems still remain to be solved, such as the amount of N–S convergence in the Occidental Alps, the repartition of the deformation between the Alpine tectonic units, and the relation between deformation and rotation across the Alpine arc. In order to address these problems, the GPS ALPES group, made up of French, Swiss and Italian research organizations, has achieved the first large-scale GPS surveys of the Western Alps. More than 60 sites were surveyed in 1993 and 1998 with a minimum observation of 3 days at each site. GPS data processing has been done by three independent teams using different software. The different solutions have horizontal repeatabilities (N–E) of 4–7 mm in 1993 and 2–3 mm in 1998 and compare at the 3–5-mm level in position and 2-mm/yr level in velocity. A comparison of 1993 and 1998 coordinates shows that residual velocities of the GPS marks are generally smaller than 2 mm/yr, precluding a detailed tectonic interpretation of the differential motions. However, these data seem to suggest that the N–S compression of the Western Alps is quite mild (less than 2 mm/yr) compared to the global convergence between the African and Eurasian plate (6 mm/yr). This implies that the shortening must be accomodated elsewhere by the deformation of the Maghrebids and/or by rotations of Mediterranean microplates. Also, E–W velocity components analysis supports the idea that E–W extension exists, as already suggested by recent structural and seismotectonic data interpretation. Received: 27 November 2000 / Accepted: 17 September 2001     

Free vibrations of coupled shear walls

The continuous connection method of analysis is extended to deal with the free vibrations of a coupled shear wall structure. The natural modes and frequencies are determined from the Galerkin technique, and the dynamic response following an imposed lateral displacement is evaluated. A comparison is made between theoretical predictions of natural frequencies and the results from tests on model structures.     

Analysis of photosynthetic picoeukaryote community structure along an extended Ellett Line transect in the northern North Atlantic reveals a dominance of novel prymnesiophyte and prasinophyte phylotypes

Photosynthetic picoeukaryotes (PPEs) of a size <3 ??m can contribute significantly to primary production. Here, PPE community structure was analysed along an extended Ellett Line transect, an area in the North Atlantic well studied by physical oceanographers but largely neglected in the field of microalgal ecology. Distribution patterns of specific PPE classes were determined using dot-blot hybridization analysis, while the taxonomic composition of specific PPE classes was revealed by phylogenetic analysis of plastid 16S rRNA gene sequences. In addition, we performed fluorescent in situ hybridization (FISH) analysis of seawater samples collected along the transect to provide a PCR-independent survey of class level PPE distribution patterns. We found the PPE community was dominated by members of the Prymnesiophyceae, Prasinophyceae and Mamiellophyceae. Interestingly, phylogenetic analysis revealed several novel Prymnesiophyceae and Prasinophyceae phylotypes (with only 85-96% identity to neighbouring sequences) within lineages for which cultured counterparts are unknown.     

Heat,volume and chemical fluxes from submarine venting: A synthesis of results from the Rainbow hydrothermal field, 36°N MAR

High-temperature hydrothermal activity occurs in all ocean basins and along ridge crests of all spreading rates. While it has long been recognized that the fluxes associated with such venting are large, precise quantification of their impact on ocean biogeochemistry has proved elusive. Here, we report a comprehensive study of heat, fluid and chemical fluxes from a single submarine hydrothermal field. To achieve this, we have exploited the integrating nature of the non-buoyant plume dispersing above the Rainbow hydrothermal field, a long-lived and tectonically hosted high-temperature vent site on the Mid-Atlantic Ridge. Our calculations yield heat and volume fluxes for high-temperature fluids exiting the seafloor of ～0.5 GW and 450 L s^?1, together with accompanying chemical fluxes, for Fe, Mn and CH₄ of ～10, ～1 and ～1 mol s^?1, respectively. Accompanying fluxes for 25 additional chemical species that are associated with Fe-rich plume particles have also been calculated as they are transported away from the Rainbow vent site before settling to the seabed. High-temperature venting has been found to recur at least once every ～100 km along all slow-spreading ridges investigated to-date, with half of all known sites on the Mid-Atlantic Ridge occurring as long-lived and tectonically hosted systems. If these patterns persist along all slow- and ultraslow-spreading ridges, high-temperature venting of the kind reported here could account for ～50% of the on-axis hydrothermal heat flux along ～30,000 km of the ～55,000 km global ridge crest.